Evolution of defects and their effect on photoluminescence and conducting properties of green-synthesized ZnS nanoparticles

We have grown ZnS (zinc sulfide) nanoparticles (NPs) by hydrothermal and microwave (MW) heating method and a comparative study on the physical properties was carried out. Zinc acetate dihydrate (ZAD) and thioacetamide (TA) were used as Zn and S precursors, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) pattern revealed the cubic structure for ZnS and nanocrystalline nature of the samples. The careful observation of the XRD patterns of the samples grown by hydrothermal and microwave heating method indicate that microwave-synthesized ZnS (ZnS-MW) samples were strained compared to those grown by conventional hydrothermal methods. Uniform sized smaller nanoparticles were formed during microwave irradiation in a much shorter time. UV-Vis absorption spectra indicated quantum confinement effect. The emission peaks in photoluminescence spectra indicate the presence of various point defects in the samples. In the microwave synthesized sample, nucleation and growth process of the ZnS crystallites are very quick, leading to the formation of defects. The dielectric studies of both types of the samples show a typical behavior of polycrystalline semiconducting material. Under the applied A.C. fields, the conduction phenomena provide sufficient evidence for the electronic hopping between localized sites. Lower values of activation energy obtained for both dipolar relaxation and DC conductivity in the case of microwave synthesized sample indicate the applicability of such materials in various switching applications.